1. Field of the Invention
The present invention relates to a frequency synthesizer, and more particularly to a frequency synthesizer for receiving and sending signals in a wideband wireless communication system receiving and sending data in multiple bands.
2. Description of the Related Art
In general, in the wireless communication systems, the transmitters use one or more carrier signals to convert one or more base-band information signals into a radio frequency (RF) signal for transmissions, and the receivers eliminate a carrier signal from a received RF signal, convert the resultant signal into an intermediate frequency (IF) signal, and demodulate the IF signal or directly demodulate the RF signal without the conversion into the RF signal.
The wireless communication system uses frequencies in a certain frequency band in order to send data. However, as more data is sent through the wireless communication system, the frequency band also increases. Such a wide frequency band is referred to as the Ultra Wide Band (UWB).
Since the wireless communication system uses a carrier frequency to send data to a receiver, the wireless communication system first generates the carrier frequency to send data.
The communication system uses a local oscillator (LO) to generate a frequency for data transmissions. That is, the communication system uses a signal generated from the local oscillator to send data, or first performs a certain process if the signal generated from the local oscillator is not a proper signal. In other words, the communication system uses a specific signal to perform a certain process with a signal generated from the local oscillator, so as to generate a proper signal. Hereinafter, a signal generated from the local oscillator is referred to as a local oscillation signal (LO signal).
The UWB communication system divides the UWB into plural frequency sub-band of a certain bandwidth, and uses the plural frequency sub-bands to send data for a specific time period, so as to send lots of data for the specific time period. Such an UWB communication system generally uses the intermediate frequencies (IFs) 3432 MHz, 3960 MHz, and 4488 GHz of three frequency sub-bands. Thus, the UWB communication system uses a signal generated from the local oscillator to generate the intermediate frequencies of the three frequency sub-bands.
FIG. 1 is a view for showing a general frequency synthesizer for generating the intermediate frequencies of the three frequency sub-bands.
The frequency synthesizer shown in FIG. 1 is built in a structure used in the direct conversion multi-band orthogonal frequency division multiplexed (OFDM) UWB system, and has frequency even-dividers and plural SSB mixers. Further, the oscillation frequency of the local oscillator 10 is set to 4224 MHz in order for the UWB system to generate the intermediate frequencies of the three frequency sub-bands through the even frequency divisions. The phase locked loop (PLL) 20 stabilizes a reference frequency generated from the local oscillator 10.
The two frequency dividers 30 and 40 use a reference frequency of 4224 MHz generated from the local oscillator 10 so as to generate control frequencies of 528 MHz and 264 MHz, and the first single side band (SSB) mixer 50 mixes the control frequencies of 528 MHz and 264 MHz so as to generate a control frequency of 792 MHz.
The selection unit 60 selectively inputs the generated control frequencies of 264 MHz and 792 MHz to the second SSB mixer 70, and the second SSB mixer 70 mixes the reference frequency of 4224 MHz generated from the local oscillator 10 with the control frequencies of 264 MHz and 792 MHz input from the selection unit 60, so as to generate three center frequencies of 4488 MHz, 3960 MHz, and 3432 MHz.
In the frequency synthesizer shown in FIG. 1, the signal generated from the local oscillator 10 is a Quadrature signal containing the I and Q signals, but the structure shown in FIG. 1 lacks detailed components for generating the Quadrature signal. Further, FIG. 1 does not show details on the structures of the SSB mixers, and reveals a problem of difficulties in estimating electric power consumption.
Meanwhile, FIG. 2 is a view for showing another general frequency synthesizer for generating center frequencies of the three frequency sub-bands.
The frequency synthesizer shown in FIG. 2 has a structure used in the Double-Conversion multi-band OFDM UWB system, uses plural frequency dividers to enable the synthesizing of double-conversion frequencies, and uses two Poly-Phase Filters (PPFs) to generate a Quadrature signal for synthesizing frequencies of SSB mixers. Further, the oscillation frequency of the local oscillator 110 of the UWB system is set to 2640 MHz in order that the center frequencies of the three frequency sub-bands are generated. Further, the oscillation frequency of the local oscillator 110 is set to 2640 MHz in order that the UWB system generates the center frequencies of the three frequency sub-bands. Furthermore, the phase locked loop (PLL) 130 stabilizes the reference frequency generated from the local oscillator 110.
The two frequency dividers 120 and 140 uses the reference frequency of 2640 MHz generated from the local oscillator 110 to generate the control frequencies of 1320 MHz and 528 MHz, and the first and second PPF 150 and 160 control the phases of signals of 528 MHz and 2640 MHz to generate Quadrature signals. Further, the SSB mixer 170 mixes the Quadrature signals of 528 MHz and 2640 MHz to generate 2112 MHz and 3168 MHz frequencies.
The generated signals of 2112 MHz and 3168 MHz are input to the switch 180, and the switch 180 outputs either the 2640 MHz signal generated from the local oscillator 110 or any of the 2112 MHz and 3168 MHz signals as a first output signal of the frequency synthesizer. Further, the 1320 MHz signal generated from the frequency divider 120 is output as a second output signal of the frequency synthesizer, and the first and second output signals are used together for generation of the RF signal at the transmitter side and for restoration of the IF signal at the receiver side.
The frequency synthesizer shown in FIG. 2 uses the two PPFs to generate the Quadrature signals for mixing frequencies at the SSB mixer with respect to the signals generated from the local oscillator 110, but, in its structure, the frequency synthesizer has to have additional buffers to compensate for signal attenuation caused by the operations of the PPFs, which causes a problem of more power consumption.